1. Field of the Invention
The present invention relates generally to an apparatus and method for estimating a channel condition in a mobile communication system, and in particular, to an apparatus and method for estimating a channel condition of a forward link in an Orthogonal Frequency Division Multiplexing (OFDM) communication system using multiple carriers.
2. Description of the Related Art
Generally, an OFDM communication system is a multi-carrier transmission system that transmits data using several carriers that are orthogonal with each other. This system is distinguished from a single-carrier transmission system that transmits data using a single carrier. In such a multi-carrier transmission system, each carrier has a very short bandwidth and it is considerably affected by a variation in a channel. However, when it comes to the overall frequency band, in the case of a multipath interference channel, transmission carriers suffer reduction only in their amplitude due to a variation in the channel, so they can be satisfactorily recovered.
Commonly, in a radio communication environment, a condition of a forward channel is changed according to several factors such as velocity and a surrounding environment of a mobile station. In the OFDM communication system, adaptive transmission techniques for increasing system efficiency, such as PCR (Per Carrier Rate Control), AUA (Adaptive User Allocation), and Adaptive Modulation, are used in a base station according to such a time-varying channel condition. In order to use these adaptive techniques, it is necessary to estimate a condition of a forward channel. The forward channel condition can be estimated through a carrier-to-interference ratio (C/I). However, estimating a condition of a forward channel by a base station requires a process in which a mobile station measures C/I using a forward pilot channel by Frequency Division Duplexing (FDD) and feeds back the measured C/I to the base station.
In addition, because the OFDM communication system uses a plurality of subcarriers, feedback information used for feeding back information on a channel condition of each subcarrier greatly increases in quantity. Such feedback information transmitted via a reverse link serves as an overhead on the reverse link and greatly reduces efficiency of the reverse link.